add matplotlib journey course to external resources

Author: JosephBARBIERDARNAL

doc/users/resources/index.rst

@@ -82,6 +82,10 @@ Tutorials
   <https://github.com/stefmolin/python-data-viz-workshop>`_
   by Stefanie Molin
 
+* `Matplotlib Journey: Interactive Online Course
+  <https://www.matplotlib-journey.com/>`_
+  by Yan Holtz and Joseph Barbier
+
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 Galleries
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